1. Field of the Invention
The present disclosure generally relates to a multi-step exposed image acquisition method by an electronic shutter and a photography apparatus using the same, and more particularly, to a multi-step exposed image acquisition method which controls the timing of a reset pulse and a lead-out pulse of an image sensor and a photography apparatus using the same.
2. Description of the Related Art
A shutter of a camera may be generally classified as a lens shutter which is located in the vicinity of a lens or as a focal plane shutter which is located in the vicinity of a focal plane.
The focal plane shutter includes two types, i.e., a left and right type shutter and an up and down type shutter, according to travel directions of front and rear curtains. The up and down type shutter which is advantageous in terms of performance has been mainly used.
In a photography apparatus adopting the focal plane shutter, two curtains including the front and rear curtains travel to expose an image of a subject onto a plane. In other words, the photography apparatus uses a method for exposing the plane to light from the lens of the photography apparatus due to the travel of the front curtain to start an exposure and the travel of the rear curtain at a time interval due to a preset shutter speed to end exposure.
However, many techniques for electronically processing a front curtain of a focal plane shutter have been suggested in order to solve problems of a mechanical shutter, e.g., a front curtain shock caused by shock vibrations during the travel of the front curtain, a release time lag necessary for charging the front curtain, etc.
In other words, an electronic shutter has been used to sequentially scan pixel lines using a reset signal, which causes pixels to begin to be exposed to light in a charge-coupled device (CCD) or a complementary metal oxide semiconductor (CMOS) image sensor (CIS) of a photography apparatus, and thus replace a role of a front curtain.
In general, a photography apparatus using an electronic shutter includes an auto focus (AF) system and an auto exposure (AE) system. The AF system automatically adjusts a focus of a subject, i.e., analyzes contrast of an image obtained through an image sensor to automatically adjust the focus. The AE system determines the brightness of the subject to automatically determine an exposure, i.e., controls opening/closing of an iris and a speed of a shutter with respect to an appropriate exposure amount of the subject to automatically adjust an appropriate exposure.
However, if the brightness of a subject changes gradually, it is not easy to give appropriate exposure to all areas.